Active stylus downlink signal transmission timing control relative to sensor controller

ABSTRACT

A method in which a sensor controller is connected to a sensor having an electrode group provided together with a display panel configured to operate in during a variable refresh cycle among a plurality of refresh cycles, and an active stylus performs bidirectional communication with the sensor controller. According to the method, the sensor controller acquires a present refresh cycle among the plurality of refresh cycles of the display panel, generates an uplink signal, which serves as a reference for synchronization corresponding to the acquired present refresh cycle, and transmits the uplink signal to the active stylus, which is not detected as yet or is detected already, at the present refresh cycle.

BACKGROUND Technical Field

The present disclosure relates to a method in which an active stylus anda sensor controller are used, a system, a sensor controller, and anactive stylus.

Description of the Related Art

In recent years, as an inputting apparatus for hand-written inputting ona panel of an electronic apparatus, styluses of various types such asthe electromagnetic induction type and the capacitance type have beengetting used, and a stylus of an active capacitive type is one of suchstyluses. In the following description, a stylus of the activecapacitive type is referred to as “active stylus.”

Transmission of a signal by an active stylus is performed by supplying atransmission signal to an electrode provided at a tip of the activestylus such that a variation of an electric field (alternating electricfield) is generated in a space in the proximity of the electrode. Anelectronic apparatus includes a sensor board including an electrodegroup disposed in a matrix below a panel and a sensor controllerconnected to the sensor board, and is configured such that the sensorcontroller detects a variation of a charge amount generated in theelectrode group in the sensor board by the alternating electric field toreceive a signal transmitted from the active stylus. Patent Document 1discloses an example of an active stylus configured such that ittransmits a signal modulated with writing pressure information, a uniqueidentifier (ID) and so forth together with a non-modulated continuoussignal for position detection. In the following description, anon-modulated signal for position detection is referred to as “positionsignal,” and a signal modulated with writing pressure information, aunique ID and so forth is referred to as “data signal.”

It is possible for a sensor controller of an electronic apparatuscompatible with an active stylus of the active capacitive type also totransmit a signal to the active stylus. The sensor controller supplies atransmission signal to an electrode group that configures a sensor boardthereby to generate an electric field on a panel such that a signal canbe transmitted toward the stylus. The active stylus is configured suchthat it detects a variation of the charge amount induced in theelectrodes by the electric field by the reception electrodes thereby todetect the signal transmitted from the electronic apparatus. PatentDocument 2 discloses an example of an active stylus that receives asignal transmitted from a sensor controller.

A sensor board for detecting an active stylus frequently serves also asa sensor board for detecting a touch of a finger therewith. Anelectronic apparatus is configured such that a single sensor board forperforming detection of a touch of a finger and detection of an activestylus is placed on a liquid crystal panel supplied from a displaymaker. A system in which a sensor board for performing detection of anactive stylus is placed outside a liquid crystal panel in this manner isreferred to as system of the “out cell type” for the convenience ofdescription.

It is known that, even where a sensor board exists outside a liquidcrystal panel as in a system of the out cell type, a driving signal inthe liquid crystal panel existing below the sensor board makes a noiseand has an influence on a detection action of a finger by the sensorcontroller or on a detection action of the active stylus. Arepresentative one of types of such noise is an alternating currentcomponent of a voltage signal supplied to an electrode for driving apixel of the liquid crystal panel. The voltage signal is used to controlthe orientation of the liquid crystal in each pixel, and enters anelectrode group that configure the sensor board through alternatingcurrent (AC) coupling and makes noise.

A disclosure is known in which a countermeasure against such noise isperformed solely by a sensor controller. Patent Document 3 disclosesthat a signal from which noise is cancelled can be obtained by adifferential signal between a signal detected by an electrode in touchdetection of a finger and a signal detected by a dummy electrodeprovided around the electrode and including a noise component. PatentDocument 4 discloses a method in which a horizontal synchronizing pulseof a display apparatus is generated in a known cycle while the phasethereof is controlled and a position signal or a data signal from afinger or a stylus is detected from a timing synchronized with thepulse. Further, Patent Document 2 discloses that a stylus measures thelevel of a reception signal and a signal and a noise are identified fromeach other on the basis of a time length of a period within which thelevel is high.

Further, in recent years, a liquid crystal panel that performs touchdetection of a finger of the on cell type or the in cell type has becomepopular (refer to Non-Patent Document 1). In the liquid crystal panel ofthe on cell type, an electrode group for a touch sensor is arranged on acolor filter glass plate or a substrate glass plate in the inside of theliquid crystal panel, and electrodes configuring the liquid crystalpanel and electrodes configuring the sensor board are separateelectrodes. Since the distance between the electrodes is smaller thanthat of the out cell type described hereinabove, the electrodes for thetouch sensor are influenced significantly by noise from the electrodesfor liquid crystal driving.

On the other hand, in a liquid crystal panel of the in cell type, acommon electrode or a pixel electrode (hereinafter referred to ascommonly used electrode) of the liquid crystal panel is used as part ofan electrode group for touch detection of a finger or for detection ofan active stylus. While a driving action of pixels is performed in theliquid crystal panel, the potential of the commonly used electrode thatis used commonly also for touch detection is set to a potential forpixel driving (which may be fixed or may be variable). Accordingly, inthe liquid crystal panel of the in cell type, in the first place, whilea driving action of pixels is being performed, the sensor controllercannot receive a signal from the active stylus.

PRIOR ART DOCUMENTS Patent Documents

-   Patent Document 1: PCT Patent Publication No. WO2015/111159-   Patent Document 2: U.S. Patent Application Publication No.    2013/0106797-   Patent Document 3: Japanese Patent Laid-Open No. 1993-6153-   Patent Document 4: PCT Patent Publication No. WO2015/141349

Non-Patent Document

-   Non-Patent Document 1: “In cell/on cell strategy for smartphones of    JDI, LG, Sharp is read,” [online], Nikkei Technology Online,    [searched on Mar. 8, 2016], Internet <URL:    http://techon.nikkeibp.co.jp/article/NEWS/20150121/400160/>

BRIEF SUMMARY Technical Problem

In detection of a touch of a finger, even if a sensor controller solelystops a detection action of a touch of a finger within a period withinwhich much noise is generated in a system of the out cell type (or ofthe on cell type) or within a liquid crystal driving period of a liquidcrystal panel of the in cell type (those periods are hereinafterreferred to each as “display refresh period”), although a detection rateof a position signal drops, missing of information does not occur. Thisis because, as long as a finger exists on the sensor board exceeding asingle display refresh period equal to or smaller than severalmilliseconds, information indicating that a finger exists (or does notexist) does not suffer from missing.

However, if, in detection of an active stylus that transmits a datasignal modulated with data of a writing pressure value, a unique ID orthe like, the sensor controller uniquely stops a detection action withinthe period in response to a generation situation of liquid crystal noiseor an action situation thereof, then a case occurs in which part ofinformation transmitted from the active stylus within the period cannotoccasionally be transmitted. For example, when the active styluscontinues to repetitively transmit a position signal and a data signallike the active stylus disclosed in Patent Document 1, if the datasignal is received within a display refresh period, then part of dataincluded in the data signal will miss.

Especially, a sensor controller in which an electrode commonly used witha touch sensor is provided in the inside of a liquid crystal panel ofthe in cell type and is utilized comes to have an increased variety inregard to an appearance frequency and a length of a display refreshperiod in response to an action mode of the liquid crystal panel, arefresh rate, various action modes regarding in which region a commonlyused electrode is used for driving of a pixel and so forth, settings,and a configuration of electrodes. Further, similarly to a liquidcrystal panel of the in cell type, within what period a display refreshperiod appears in display panels such as an organic electroluminescence(EL) panel in which some of driving electrodes are commonly used with atouch sensor or a display panel of a special shape used together with adigital signage or the like depends upon a configuration and action ofthe display panels.

In order to make it possible for a sensor controller, which isincorporated in a system that uses a display panel of the in cell typeor a display panel that acts in various display refresh periods, todetect a signal transmitted from an active stylus, which is in a pendown operation state, as soon as possible and receive information of awriting pressure and so forth put on a data signal without missing inthe future, it is desirable to make it possible to transmit a preferabletransmission timing for a signal in response to a refresh or a settingstate of the display panel from the sensor controller to the activestylus such that the active stylus can transmit a predetermined signalavoiding a display refresh period unique to the display panel.

Accordingly, one object of the present disclosure resides in provisionof a method in which an active stylus and a sensor controller are used,a system, a sensor controller, and an active stylus by which apreferable transmission timing of a signal according to a refresh stateof a display panel can be conveyed from a sensor controller to an activestylus.

Technical Solution

A method according to the present disclosure in which a sensorcontroller is connected to a sensor having an electrode group providedtogether with a display panel configured to operate in a variablerefresh cycle among a plurality of refresh cycles, and an active stylusperforms bidirectional communication with the sensor controller.According to the method, the sensor controller acquires a presentrefresh cycle among the plurality of refresh cycles of the displaypanel, generates an uplink signal, which serves as a reference forsynchronization corresponding to the acquired refresh cycle, andtransmits the uplink signal to the active stylus, which is not detectedas yet or is detected already, at the present refresh cycle.

A system according to the present disclosure includes a sensorcontroller connected to a sensor having an electrode group providedtogether with a display panel configured to operate in a variablerefresh cycle among a plurality of refresh cycles, and an active stylusthat performs bidirectional communication with the sensor controller.The sensor controller transmits an uplink signal, which serves as areference for synchronization corresponding to the present refresh cycleamong the plurality of refresh cycles of the display panel and serves asa reference that designates a time point at which the active stylus isto transmit a downlink signal, to the active stylus that is not detectedas yet or is detected already at the refresh cycle. The active stylus,in operation, detects the uplink signal, transmits the downlink signalat the time point designated by the reference included in the detecteduplink signal. The sensor controller detects the active stylus bydetecting the downlink signal.

A sensor controller according to the present disclosure is connected toa sensor having an electrode group provided together with a displaypanel configured to operate in a variable refresh cycle among aplurality of refresh cycles and perform bidirectional communication withan active stylus. The sensor controller includes a transmission circuit,and a control circuit that, in operation, specifies a present refreshcycle among the plurality of refresh cycles of the display panel andcauses the transmission circuit to transmit an uplink signal, whichserves as a reference for synchronization of a transmission of adownlink signal corresponding to the specified refresh cycle, to theactive stylus.

An active stylus according to the present disclosure performsbidirectional communication with a sensor controller connected to asensor having an electrode group provided together with a display panelthat displays images during a plurality of refresh cycles. The activestylus includes a reception circuit that, in operation, receives fromthe sensor controller an uplink signal that serves as makes a referencefor synchronization transmitted repetitively at a present refresh cycleamong the plurality of refresh cycles of the display panel, and atransmission circuit that, in operation, transmits a downlink signal tothe sensor controller at a time point designated by the uplink signal.

Advantageous Effect

According to the present disclosure, since the sensor controlleracquires a signal indicating a present refresh cycle of the displaypanel, it is possible to transmit, from the sensor controller to theactive stylus, an uplink signal that serves as a reference tosynchronization corresponding to the refresh cycle indicated by theacquired signal. Accordingly, to the active stylus that sends back adownlink signal at a timing designated as a reference time point forsynchronization given by the uplink signal or transmits a downlinksignal cyclically, a preferable transmission timing for a signalaccording to a state of the display panel can be conveyed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view of a position inputting system 1 according toa first embodiment of the present disclosure.

FIG. 2 is a schematic block diagram depicting functional blocks of astylus 2 depicted in FIG. 1.

FIG. 3 is a schematic block diagram depicting functional blocks of asensor controller 31 depicted in FIG. 1.

FIG. 4 is a view illustrating an example of a relationship between adriving signal LD and liquid crystal noise LCDnz depicted in FIG. 1.

FIG. 5 is a view depicting a display face of a liquid crystal panel 33depicted in FIG. 1.

FIG. 6 is a view illustrating another example of the relationshipbetween the driving signal LD and the liquid crystal noise LCDnzdepicted in FIG. 1.

FIG. 7 is a view depicting a relationship between a refresh rate Rr ofthe liquid crystal panel 33 and a transmission cycle of an uplink signalUS.

FIG. 8 is a table (communication resource table CRTbl) indicative ofrefresh cycles VT of the liquid crystal panel 33 and communicationsituations of the position inputting system 1.

FIGS. 9A and 9B are schematic views depicting a structure of a liquidcrystal panel 33 serving also as a sensor board 34 according to a secondembodiment of the present disclosure.

FIG. 10 is a schematic block diagram depicting functional blocks of acontrol device 60 according to the second embodiment of the presentdisclosure.

FIG. 11A is a view depicting an example of arrangement of a blank periodBPa according to the second embodiment of the present disclosure, andFIGS. 11B and 11C are views depicting a manner of use of the blankperiod BPa of FIG. 11A by an indicator detection circuit 62 depicted inFIG. 10.

FIG. 12 is a view depicting an example of a configuration of an uplinksignal US illustrated in FIGS. 11A, 11B, and 11C.

FIG. 13 is a view depicting an example of the uplink signal US and adownlink signal DS in the case where a stylus 2 performs transmission ofa data signal OD_DP within a time period T6.

FIGS. 14A and 14B are views depicting particular examples of datatransmitted within a time period secured for transmitting a data signalOD_DP.

FIG. 15 is a processing flow diagram depicting a process performed bythe indicator detection circuit 62 depicted in FIG. 10.

FIG. 16 is a processing flow diagram illustrating details of a datareception process performed at S8 depicted in FIG. 15.

FIG. 17 is a processing flow diagram illustrating a process performed bythe stylus 2 depicted in FIG. 10.

MODES FOR CARRYING OUT THE DISCLOSURE

In the following, embodiments of the present disclosure are described indetail with reference to the accompanying drawings. First, as a firstembodiment, a case in which the present disclosure is applied to asystem of the out cell type is described. Thereafter, as a secondembodiment, a case in which the present disclosure is applied to asystem of the in cell type is described.

FIG. 1 is a schematic view of a position inputting system 1 according tothe first embodiment of the present disclosure. The position inputtingsystem 1 is a system that utilizes a stylus of the active capacitivetype. The position inputting system 1 is configured including a stylus 2(active stylus) for inputting an indication position P (P0 through Pkthrough Pn) and operation state data OD of a writing pressure and soforth to the electronic apparatus 3, and a sensor controller 31 thatderives an indication position P of the stylus 2 at present using asensor board 34 placed on the liquid crystal panel 33 and outputs theindication position P to an electronic apparatus control circuit 30together with the operation state data OD. The sensor controller 31 isprovided in the electronic apparatus 3 that includes a liquid crystalpanel 33 and a liquid crystal driving circuit 32, and an electronicapparatus control circuit 30 that controls the liquid crystal panel 33and the liquid crystal driving circuit 32.

The stylus 2 is a stylus of the active capacitive type including a powersupply, a communication circuit and electrodes for detecting an uplinksignal US transmitted in a predetermined cycle from the sensorcontroller 31 and transmitting a downlink signal DS at a time pointindicated as a reference time point given by the detected uplink signalUS. The indicated time point is either (1) a time point designated inadvance before the sensor controller 31 detects the stylus 2(hereinafter determined as time point immediately after the uplinksignal US) or, after the stylus 2 and the sensor controller 31 detecteach other, (2) a time point designated expressly as a reference timepoint given by the uplink signal US in accordance with a command CC_UPincluded in the uplink signal US.

The downlink signal DS includes a position signal D_DP indicating thatthe stylus 2 exists at a position at which it is detected and a datasignal OD_DP modulated with data such as operation state data OD or thelike such as writing pressure information. The position signal D_DP isutilized also as a response signal with which the stylus 2 responds toan uplink signal US hereinafter described transmitted from the sensorcontroller 31 to allow the sensor controller 31 to detect the stylus 2.In the following description, where the position signal D_DP and thedata signal OD_DP are not distinguished from each other, they arecollectively referred to as downlink signal DS.

The sensor controller 31 is an integrated circuit (IC) that is connectedto the sensor board 34 provided in an opposing relationship to theliquid crystal panel 33 in a normal direction to the liquid crystalpanel 33 and performs communication with the stylus 2 through the sensorboard 34. The sensor controller 31 manages the cycle and the time periodfor transmitting an uplink signal US on the basis of a refresh state ofthe liquid crystal driving circuit 32, transmits an uplink signal US inaccordance with the cycle and the time period, and detects a downlinksignal DS transmitted at a reference time point given by the uplinksignal US, thereby detecting the stylus 2. Further, the sensorcontroller 31 derives an indication position P of the stylus 2 on thebasis of the detection position, extracts operation state data OD of awriting pressure and so forth from data included in the data signalOD_DP and supplies the operation state data OD to the electronicapparatus control circuit 30 together with the indication position P.

The liquid crystal panel 33 includes a plurality of pixels arranged in amatrix along two directions in which a panel face is formed (an Xdirection and a Y direction depicted in FIG. 1). Each pixel isconfigured including a pixel electrode and liquid crystal. The liquidcrystal panel 33 is configured further including a polarizer, a glasssubstrate, a color filter, a common electrode, a backlight light sourceand so forth. Among the components mentioned, the common electrode isprovided for each region where the panel face is divided into aplurality of regions, and within a display refresh period, a fixed orvariable voltage is applied to the common electrode such that apotential difference according to a value of a pixel is formed betweenthe common electrode and the pixel electrode.

The liquid crystal driving circuit 32 generates a driving signal LD(gate-source voltage or the like) on the basis of a video signal Vsupplied from the electronic apparatus control circuit 30. The drivingsignal LD plays a role of controlling polarization of liquid crystal ofeach pixel in the liquid crystal panel 33 to display a video imageaccording to the video signal V. The driving signal LD includes acomponent of a high frequency, and every time the driving signal LD issupplied to the liquid crystal panel 33, liquid crystal noise LCDnz isincluded also in a signal to be received by the sensor controller 31through a parasitic capacitance (represented by C2 in FIG. 1) formedbetween the liquid crystal panel 33 and the sensor board 34.

Now, an outline of action of the position inputting system 1 isdescribed in light of a typical operation method of the stylus 2 by auser.

When the stylus 2 is to be operated, the user would perform an operationfor moving the stylus 2 toward an operation panel 35 (pen downoperation). The movement of the stylus 2 by the pen down operation is aspace movement including a component in a normal direction to theoperation panel 35 (Z direction depicted in FIG. 1). When the stylus 2comes near to the sensor board 34 in the proximity of an indicationposition P0 as depicted in FIG. 1, a sufficient coupling capacitance Cfor transmitting and receiving a signal is formed between an electrodegroup configuring the sensor board 34 and a tip of the stylus 2. Thestylus 2 is enabled to detect an uplink signal US transmitted from thesensor controller 31 through the coupling capacitance C. The stylus 2performs an internal process for synchronizing with the uplink signal USand transmits a downlink signal DS at a time point designated by thesensor controller 31 with reference to a reference time point given bythe uplink signal US (for example, at a time point immediately after thereference time point). If the sensor controller 31 successfully receivesa downlink signal DS transmitted from the stylus 2 without beinginfluenced by noise LCDnz or the like, then the sensor controller 31 canstart processes for detection of the stylus 2, derivation of theindication position P and so forth.

After the pen down operation, the user would move the tip of the stylus2 in such a manner as to draw a locus Path, for example, from P0 to Pndepicted in FIG. 1 in a state in which the tip of the stylus 2 is keptin contact with the operation panel 35. During the period, the stylus 2repeats transmission of a position signal D_DP and a data signal OD_DPat each time point indicated on the basis of the reference time pointgiven by the uplink signal US. Within the period, the value of thecoupling capacitance C has a comparatively high value in comparison withthat upon pen down.

The user would perform an operation for removing the tip of the stylus 2from the operation panel 35 (pen up operation). The pen up operation isan operation reverse to the pen down operation. If the sensor controller31 and the stylus 2 are spaced away from each other to such a degreethat a sufficient coupling capacitance C is not formed any more in theproximity of the indication position Pn, then transfer of a signalbetween the stylus 2 and the sensor controller 31 is disabled. Evenafter the transfer is disabled, for a fixed time period, the referencetime point and the cycle are maintained as an internal state of each ofthe stylus 2 and the sensor controller 31. After the fixed time periodelapses, the reference time point as an internal state of each thestylus 2 and the sensor controller 31 is canceled.

If the sensor controller 31 fails to detect a downlink signal DStransmitted from the stylus 2 because of liquid crystal noise LCDnzalthough the stylus 2 undergoes a pen down operation and exists within adetectable range irrespective of whether this is caused by the fact thatthe stylus 2 cannot detect an uplink signal US or by the fact that adownlink signal DS sent back from the stylus 2 cannot be detected by thesensor controller 31, then the time point at which the sensor controller31 detects the stylus 2 is delayed at least to next transmission of anuplink signal US.

That detection of the stylus 2 by the sensor controller 31 is delayedcauses a delay of succeeding processes such as, for example, acoordinate detection process by the sensor controller 31, a cursordisplaying process of a coordinate position by the electronic apparatuscontrol circuit 30 and so forth. Here, the time point at which thestylus 2 performs the pen down operation is a time point at which theuser starts utilization of the stylus 2 on the operation panel 35, andthe delay of a succeeding displaying process causes a response delay ofthe position inputting system 1, which is experienced by the user.

Therefore, it is an object of the present embodiment that, when the userperforms a pen down operation of the stylus 2 until the stylus 2 entersthe detectable range of the sensor controller 31, the sensor controller31 can detect the stylus 2 at an early stage with a higher probability.

In particular, the sensor controller 31 transmits an uplink signal US ina cycle (refresh cycle VT) of a refresh of the liquid crystal panel 33to the stylus 2 such that a downlink signal DS is transmitted from thestylus 2 after every generation cycle of a blank period BP within whichthe amount of the liquid crystal noise LCDnz is comparatively small.

FIG. 2 is a schematic block diagram depicting function blocks of thestylus 2. As depicted in FIG. 2, the stylus 2 is configured including anelectrode 20, a transmission/reception switching circuit 21, anoscillation circuit 22, a transmission circuit 23, a reception circuit24, an operation information detection circuit 25, an operationinputting circuit 26, a configuration information storage device 27, anda communication control circuit 28.

The electrode 20 is a conductor in which charge corresponding to adownlink signal DS or an uplink signal US is induced. Thetransmission/reception switching circuit 21 is a switch for switching aconnection state between the electrode 20 and the transmission circuit23 or the reception circuit 24 on the basis of a switching signal S_selsupplied from the communication control circuit 28. Thetransmission/reception switching circuit 21 is used to perform switchingbetween transmission and reception time-divisionally.

The oscillation circuit 22 is an oscillation circuit that generates acarrier signal of a frequency to be used for communication between thesensor controller 31 and the stylus 2 on the basis of a frequencysetting signal F_sel supplied from the communication control circuit 28.The carrier signal may be a sine wave or a rectangular wave of a clockpulse.

The reception circuit 24 is configured such that it extracts a searchpattern D_UP or a command CC_UP included in a signal by detecting anddemodulating a variation (signal) of a charge amount induced in theelectrode 20 and outputs the extracted search pattern D_UP or commandCC_UP to the communication control circuit 28. Where modulation using aspread code is performed (details are hereinafter described inconnection with the second embodiment) as a modulation method for theuplink signal US, a correlation arithmetic operation between a receivedsignal and a spread code stored in advance is performed by a correlatorto extract a search pattern D_UP or a command CC_UP.

The transmission circuit 23 generates a downlink signal DS on the basisof data supplied from the communication control circuit 28 and suppliesthe downlink signal DS to the electrode 20 thereby to transmit thedownlink signal DS to the sensor controller 31. When a position signalD_DP is to be transmitted, a carrier signal provided from theoscillation circuit 22 is outputted as it is without being modulated.When a data signal OD_DP is to be transmitted, data such as theoperation state data OD, configuration data CD or the like is encoded togenerate a transmission digital signal, and a carrier signal providedfrom the oscillation circuit 22 is modulated with the transmissiondigital signal to generate a data signal OD_DP.

The operation information detection circuit 25 acquires operation statedata OD that is dynamic data that varies in response to an operationstate of the stylus 2 such as an operation state such as on/off of theoperation inputting circuit 26 that is a pushbutton or the like providedon a side face of the stylus 2, a value of a writing pressure F detectedby a writing pressure detection circuit not detected or remaining amountdata of a battery serving as a driving power supply for the stylus 2,and suitably supplies the operation state data OD to the communicationcontrol circuit 28.

The configuration information storage device 27 holds, in addition to astylus identifier SID, configuration data CD that is static data thatdoes not vary in response to an operation state of the stylus 2 such asa vendor ID indicative of a maker of the stylus 2, a type of the pen tipof the stylus 2 (ballpoint pen, brush or the like), the number ofoperation inputting circuits 26 and so forth and supplies theconfiguration data CD to the communication control circuit 28.

The communication control circuit 28 controls the transmission circuit23 such that a downlink signal DS is transmitted at a time pointindicated by the sensor controller 31 with reference to a reference timepoint given by a reception time point of an uplink signal US detected bythe reception circuit 24 after a pen down operation is started. Theindicated time point is, within a time period until the sensorcontroller 31 completes detection of a stylus 2, (1) a time pointdetermined in advance between the stylus 2 and the sensor controller 31,and particularly a time point immediately after an uplink signal USincluding a search pattern D_UP is detected (a switching gap betweentransmission and reception may be interposed). On the other hand, afterthe sensor controller 31 detects a stylus 2, the indicated point of timeis a time point designated expressly with reference to a reference timepoint given by the uplink signal US by a command CC_UP included in theuplink signal US. In the case of (2), the communication control circuit28 controls the transmission circuit 23 to transmit a data signal OD_DPincluding data designated by the command CC_UP (including operationstate data OD or configuration data CD). Further, the communicationcontrol circuit 28 holds a communication setting table and holds atiming of a reference time point detected once, a time period to be usedfor communication (time slot or the like), a frequency or the like.

FIG. 3 is a schematic block diagram depicting function blocks of thesensor controller 31. The system of the present embodiment correspondsto that of the out cell type. The sensor board 34 is placed outside(above) the liquid crystal panel 33 with a transparent adhesive layer orthe like interposed therebetween.

The sensor board 34 includes a row electrode group 45 and a columnelectrode group 46 arranged two-dimensionally in such a manner as toform a plane parallel to the operation panel 35 depicted in FIG. 1. Therow electrode group 45 and the column electrode group 46 are providedseparately from the electrodes that configure the liquid crystal panel33 (pixel electrodes and common electrodes). A signal appearing in therow electrode group 45 includes liquid crystal noise LCDnz generated inthe liquid crystal panel 33.

The sensor controller 31 is an integrated circuit connected to thesensor board 34 and is configured, as depicted in FIG. 3, including atransmission/reception switching circuit 47, an oscillation circuit 40,a transmission circuit 41, a reception circuit 42, an indicatordetection circuit 43, and a refresh cycle acquisition circuit 44.

The transmission/reception switching circuit 47 is a switch group forswitching a connection state between the electrodes configuring the rowelectrode group 45 and the transmission circuit 41 or the receptioncircuit 42 hereinafter described on the basis of a switching signalS_sel supplied from the indicator detection circuit 43. The switchingsignal S_sel is a signal for instructing, within a time period withinwhich the indicator detection circuit 43 is to transmit an uplink signalUS toward the stylus 2 (and when the indicator detection circuit 43 isto perform detection of a finger touch), the transmission/receptionswitching circuit 47 to connect the row electrode group 45 to thetransmission circuit 41, but instructing, when the indicator detectioncircuit 43 is to receive a signal from the stylus 2, thetransmission/reception switching circuit 47 to connect the row electrodegroup 45 to the reception circuit 42.

The oscillation circuit 40 is an oscillation circuit that generates asignal of a sine wave (or a rectangular wave) of a frequency based on afrequency setting signal F_sel supplied from the indicator detectioncircuit 43.

The transmission circuit 41 modulates a carrier signal provided from theoscillation circuit 40 with a search pattern D_UP and a command CC_UPsupplied from the indicator detection circuit 43 at a timing indicatedby the indicator detection circuit 43 and outputs an uplink signal US tothe row electrode group 45.

The reception circuit 42 executes a reception action of a downlinksignal DS of the indicator detection circuit 43 at a timing indicated bythe indicator detection circuit 43. If a downlink signal DS is detectedwithin a reception period, then the reception circuit 42 extractsoperation state data OD and so forth included in a data signal OD_DP andsupplies the operation state data OD to the indicator detection circuit43, and acquires position information Pos indicative of an electrode bywhich a downlink signal DS corresponding to the data signal OD_DP isreceived and supplies the position information Pos to the indicatordetection circuit 43.

The refresh cycle acquisition circuit 44 is a functioning circuit thatspecifies, on the basis of a driving signal LD or a refresh rate Rroutputted from the liquid crystal driving circuit 32, a situation of themonitored liquid crystal noise LCDnz or the like, a refresh cycle VT(refer to FIG. 7) indicative of a cycle of control of the liquid crystalpanel 33 by the liquid crystal driving circuit 32 and a blank period BP(refer to FIGS. 4 and 7) that is a period within which the appearancefrequency of the liquid crystal noise LCDnz is reduced (becomes sparsein comparison with that within any other period) within the refreshcycle VT. The blank period BP is a period remaining when a displayrefresh period is removed from the refresh cycle VT corresponding to therefresh rate Rr and is, in the present embodiment, a vertical blankingperiod VB as hereinafter described with reference to FIG. 7.

In such a position inputting system of the out cell type as depicted inFIG. 3, the liquid crystal driving circuit 32 and the sensor controller31 are configured from integrated circuits separate from each otherdesigned independently of each other, and terminals for extracting thedriving signal LD or the refresh rate Rr may not necessarily be providedon the liquid crystal driving circuit 32. Therefore, the refresh cycleacquisition circuit 44 receives supply of the driving signal LD or therefresh rate Rr from the liquid crystal driving circuit 32 when this ispossible and extracts a refresh cycle VT and a blank period BP from thedriving signal LD or the refresh rate Rr but detects, when it cannotreceive supply of the driving signal LD or the refresh rate Rr from theliquid crystal driving circuit 32, it monitors the liquid crystal noiseLCDnz to detect the density of the liquid crystal noise LCDnz thereby toextract a refresh cycle VT and a blank period BP.

The indicator detection circuit 43 allocates a communication resourcefor detecting a stylus 2 not detected as yet within a refresh cycle VTand a blank period BP acquired by the refresh cycle acquisition circuit44 and stores the communication resource into a communication resourcetable CRTbl. Further, the indicator detection circuit 43 performscontrol for transmitting an uplink signal US including a search patternD_UP for each refresh cycle VT using the allocated communicationresource.

The search pattern D_UP is data including a bit pattern known to thestylus 2 and is data in which 0 or 1 successively appears or 0 and 1repetitively appear alternately. If the uplink signal US generated bymodulation with the search pattern D_UP is a signal that provides areference timing for synchronization to the stylus 2 that is to detectthe uplink signal US, then the bit length or the substance of the searchpattern D_UP does not matter. The uplink signal US that includes asearch pattern D_UP including one bit or a plurality of bits makes asignal for instructing the stylus 2 to transmit a downlink signal DSimmediately with reference to a reference time point given by thereception time point of the uplink signal US.

The indicator detection circuit 43 may determine, on the basis of actionmode information indicative of the refresh cycle VT and the blank periodBP extracted by the refresh cycle acquisition circuit 44 or the like,one transmission cycle from among transmission cycles of a finite numberof uplink signals US set in advance for the action mode information orthe like (cycle of a time slot S0). The transmission cycle of the uplinksignal US determined from among the plurality of refresh cycles VT inthis manner makes one component of communication resources stored in thecommunication resource table CRTbl in addition to the blank period BP.

The indicator detection circuit 43 allocates, after it detects a stylus2, a time period within which a position signal D_DP and a data signalOD_DP are to be transmitted to the stylus 2 detected already and storesthe time period into the communication resource table CRTbl. Further,the indicator detection circuit 43 transmits an uplink signal US thatincludes the command CC_UP for indicating the substance of data to betransmitted such as the position signal D_DP, the data signal OD_DP orthe like and a timing at which the signals are to be transmitted fromthe stylus 2 (timing determined with reference to the reception timingof the uplink signal US) to the stylus 2.

FIG. 4 is a view illustrating an example of a relationship between thedriving signal LD and the liquid crystal noise LCDnz in a certain oneliquid crystal panel 33. A view at the upper side in FIG. 4 is a partialenlarged view of a signal waveform diagram depicted at the lower side.

The signal waveform diagram of FIG. 4 depicts an example of a result ofmeasurement of waveforms of a horizontal synchronizing signal HSYNC thatis a kind of a driving signal LD and liquid crystal noise LCDnz detectedon the sensor board 34 in response to the horizontal synchronizingsignal HSYNC. In FIG. 4, the axis of abscissa indicates the time, andthe axis of ordinate indicates the level of a signal.

The horizontal synchronizing signal HSYNC typically is a signal thatconveys a start and an end of a display period when a belt-shaped videoimage line is displayed on the liquid crystal panel 33 and is a signalin which a rising edge E1 and a falling edge E2 repetitively appear in ahorizontal synchronization cycle HI as illustrated in a view at theupper side in FIG. 4. The rising edge E1 indicates a start of a displayperiod, and the falling edge E2 indicates an end of a display period.

As described hereinabove, a high frequency component of the drivingsignal LD becomes liquid crystal noise LCDnz to the sensor board 34.Since the rising edge E1 and the falling edge E2 are locations at whichthe horizontal synchronizing signal HSYNC has a high frequency, liquidcrystal noise LCDnz is generated at the edges as depicted in the view atthe upper side in FIG. 4. More particularly, a state in which the liquidcrystal noise LCDnz is great continues over an arbitrary noise period NDfrom each the rising edge E1 and the falling edge E2. In contrast,within a period between adjacent noise periods ND, namely, within anoise-free period NF depicted in FIG. 4, the level of the liquid crystalnoise LCDnz is so small that it can be ignored.

The horizontal synchronization cycle HI is variable and sometimesindicates a generally long period or a generally short period asdepicted in a view at the lower side in FIG. 4. This arises from thefact that a non-displaying area is provided at part of the liquidcrystal panel 33. In the following, this is described in detail withreference to FIG. 5.

FIG. 5 is a view depicting a display face of the liquid crystal panel33. An outer frame in FIG. 5 indicates the whole display face, and aframe of a broken line indicates a display area DA in which a videoimage is to be displayed effectively. A region between an outer edge ofthe display face and the display area DA is a non-displaying area inwhich a video image is not actually displayed although it is included inthe display face. Portions of the non-displaying area above and belowthe display area DA are particularly indicated in FIG. 5 as verticaldirection non-displaying areas NDA by slanting lines. At least in theliquid crystal panel 33 fabricated at present, such a non-displayingarea inevitably appears. The horizontal synchronization cycle HI isrelatively short when the liquid crystal driving circuit 32 isgenerating a horizontal synchronizing signal HSYNC corresponding to thedisplay area DA but is relatively long while the liquid crystal drivingcircuit 32 is generating a horizontal synchronizing signal HSYNCcorresponding to each vertical direction non-displaying area NDA (withina vertical blanking period VB (Vertical Blanking)).

In the example of the liquid crystal panel 33 indicated by the examplein FIG. 4, the noise-free period NF is relatively short (noise-freeperiod NF_Dense depicted) while the liquid crystal driving circuit 32 isgenerating a horizontal synchronizing signal HSYNC corresponding to thedisplay area DA but is relatively long (noise-free period NF_Sparsedepicted) while the liquid crystal driving circuit 32 is generating ahorizontal synchronizing signal HSYNC corresponding to each verticaldirection non-displaying area NDA. In such a liquid crystal panel 33 asjust described, within a frame period of one image, a noise period NP(display refresh period) within which the generation frequency of liquidcrystal noise LCDnz is relatively high and at least one blank period BP(period within which the generation frequency of liquid crystal noiseLCDnz is relatively low) exist.

Here, in the example of the liquid crystal panel 33 of FIG. 4, the levelof the horizontal synchronizing signal HSYNC within the blank period BPindicates a generally high (High) state. However, this is an example tothe last, and also an example in which the level of the horizontalsynchronizing signal HSYNC within the blank period BP becomes a low(Low) state exists.

FIG. 6 is a view illustrating a relationship between the driving signalLD and the liquid crystal noise LCDnz in such an example as justdescribed. Also in this example, similarly as in the example in FIG. 4,a period within which the noise-free period NF becomes a noise-freeperiod NF_Dense corresponding to the display area DA and a period withinwhich the noise-free period NF becomes a noise-free period NF_Sparsecorresponding to a vertical direction non-displaying area NDA appearalternately as viewed on the time axis. The latter corresponds to ablank period BP in which the liquid crystal noise LCDnz is relativelysmall. Further, the level of the horizontal synchronizing signal HSYNCwithin the blank period BP is low (Low) as depicted in FIG. 6.

Although the characteristics of the driving signal LD differs accordingto the type of the liquid crystal panel 33 in this manner, for theliquid crystal noise LCDnz detected by the sensor board 34, a noiseperiod NP within which noise is generated relatively densely and a blankperiod BP within which noise is generated relatively sparsely exist in acycle of the refresh rate Rr. Further, it is expected that, within acycle of the refresh rate Rr, at least one blank period BP correspondingto the vertical blanking period VB exists. Here, the appearance intervaland the duration of the blank period BP differ depending upon therefresh rate Rr set at present in the liquid crystal panel 33.

In the following description, the refresh cycle acquisition circuit 44is configured such that it receives supply of a refresh rate Rr from theliquid crystal driving circuit 32 and selects one of a plurality ofrefresh cycles VT stored therein on the basis of a refresh rate Rrsupplied thereto. Further, the indicator detection circuit 43 has storedtherein a plurality of transmission cycles for an uplink signal US inadvance as described hereinabove and selects one of the transmissionperiods in response to the refresh cycle VT selected by the refreshcycle acquisition circuit 44. Then, transmission of an uplink signal USis performed in accordance with the selected transmission cycle.

FIG. 7 is a view depicting a relationship between the refresh rate Rr ofthe liquid crystal panel 33 and the transmission cycle of the uplinksignal US.

A period T_Rr1 depicted in FIG. 7 is a period within which the refreshrate Rr of the liquid crystal panel 33 is a first rate of 60 Hz (60 p).The refresh cycle VT of the liquid crystal panel 33 within this periodis a first refresh cycle VT1. A particular value of the first refreshcycle VT1 is the reciprocal of the first rate and is, for example, wherethe first rate is 60 Hz, approximately 16.7 milliseconds. Images P1 toP4 indicate images displayed with this period. Further, a period T_Rr2depicted in FIG. 7 is a period within which the refresh rate Rr of theliquid crystal panel 33 is, for example, a second rate of 48 Hz (48 p).The refresh cycle VT of the liquid crystal panel 33 within this periodis a second refresh cycle VT2. A particular value of the second refreshcycle VT2 is the reciprocal of the second rate and is, for example,where the second rate is 48 Hz, approximately 20 milliseconds. ImagesP11 to P13 indicate images displayed within this period.

As can be recognized from FIG. 7, an image displayed on the liquidcrystal panel 33 is updated in a cycle equal to the refresh cycle VT ofthe liquid crystal panel 33. Further, every time the image is updated, ablank period BP within which the occurrence interval of the liquidcrystal noise LCDnz is sparse appears at least once. In FIG. 7, theblank periods BP corresponding to the images P1 to P4 and P11 to P13 aredepicted as blank periods BP1 to BP4 and BP11 to BP13, respectively.

A communication resource table CRTbl depicted at the lower side in FIG.7 depicts a relationship between the refresh cycle VT and thetransmission timing of the uplink signal US. In the communicationresource table CRTbl, the horizontal direction indicates a time slot(however, only a portion is depicted schematically) and the verticaldirection indicates a communication frequency.

The sensor controller 31 is configured such that it transmits an uplinksignal US at a transmission timing 700 depicted in FIG. 7 in order todetect a stylus 2. In the example depicted in FIG. 7, the transmissiontiming 700 is transmitted using a time slot S0 in which a blank periodBP exists from within each refresh cycle VT, and accordingly, thetransmission cycle of the uplink signal US is equal to the refresh cycleVT. For example, within the period T_Rr1 within which the refresh cycleVT is the first refresh cycle VT1 (for example, approximately 16.7milliseconds), also the transmission cycle of the uplink signal US isVT1 (for example, approximately 16.7 milliseconds), but within a periodT_Rr2 within which the refresh cycle VT is the second refresh cycle VT2(for example, approximately 20 milliseconds), also the transmissioncycle of the uplink signal US is VT2 (for example, approximately 25milliseconds). Though not depicted, where the refresh rate Rr is setsuch that the refresh cycle VT becomes shorter (for example, 120 Hz or240 Hz), also the transmission cycle of the uplink signal US becomes ashorter value accordingly.

In FIG. 7, a period T_Rr_chng indicated between the period T_Rr1 and theperiod T_Rr2 indicates a time period that is required in order to changethe refresh rate Rr from the first rate to the second rate. It is to benoted that such a change of the refresh rate Rr (cycle of a renderingtiming) occurs, for example, when the action mode of the liquid crystalpanel 33 is changed to a power saving mode or the like or when thegeneration rate fps of an image frame is raised in order to performsmoother display to raise the refresh rate Rr to 120 Hz, 240 Hz or thelike.

FIG. 8 is a view illustrating an example of the communication resourcetable CRTbl that indicates a refresh cycle VT of the liquid crystalpanel 33 and a resource of communication allocated to a transmission orreception action in the position inputting system 1. In the example ofFIG. 8, communication resources are managed by frequencies f0, f1, andf2 and 20 time slots S0 to S19 as an example. This slot number variesdepending upon the refresh cycle VT.

FIG. 8 indicates a transmission timing 700 of an uplink signal USincluding a search pattern D_UP for detecting a stylus 2, a responsetiming 719 for allowing a stylus 2 not detected as yet to respond to anuplink signal US and transmission timings 701 and 702 for allowing astylus 2 detected already to transmit a position signal D_DP or a datasignal OD_DP including operation state data OD.

As depicted in FIGS. 8 and 7, the transmission timing 700 of the uplinksignal US is given to the time slot S0 within the blank period BP. Thecycle to which the transmission timing 700 is given (transmission cycleof the uplink signal US) varies depending upon the refresh rate Rr ofthe liquid crystal panel 33 and is determined once after the sensorcontroller 31 is activated or reset such that it coincides at least withone blank period BP. The sensor controller 31 performs transmission ofan uplink signal US including a search pattern D_UP for a time perioduntil a stylus 2 is detected using the time slot S0 corresponding to ablank period BP for each cycle of the refresh rate Rr.

The response timing 719 is a timing at which, after a stylus 2 detectsan uplink signal US including a search pattern D_UP, it responds to theuplink signal US immediately after a reference time point given by theuplink signal US. The reason why the uplink signal US is given to thetime slot S1 immediately after the uplink signal US is transmitted isthat it is intended to cause the response timing 719 to be included inthe blank period BP.

If a stylus 2 that is not detected by the sensor controller 31 as yetreceives the uplink signal US through the time slot S0, then ittransmits, as a response signal to the uplink signal US, a positionsignal D_DP, which is a downlink signal DS for indicating presence ofthe stylus 2 itself, through the time slot S1 immediately after then.

By fixedly setting the response timing 719 to the time slot S1immediately after the time slot S0 through the uplink signal US istransmitted, transmission of the downlink signal DS can be induced suchthat the response signal is positioned within the blank period BP sameas that of the time slot S0. Consequently, the sensor controller 31 thatdetects a stylus 2 by periodically transmitting an uplink signal US anddetecting a downlink signal DS can obtain a downlink signal DS within aperiod that is not influenced by the liquid crystal noise LCDnz as soonas possible before the stylus 2 is brought into contact with theoperation panel 35 on which the stylus 2 is being pen down operated. Itis to be noted that, if the liquid crystal noise LCDnz is not influencedby detection of an uplink signal US by the stylus 2, then only thetransmission timing 701 may be included in the blank period BP.

The transmission timing 701 indicates the time slot S2 or S4 expresslydesignated by a command CC_UP with reference to the reference time point(S0) given by the uplink signal US and the used efficiency f1 to thestylus 2 (2B) detected already. The transmission timing 702 indicatesthe time slot S3 or S5 expressly designated by the command CC_UP and theused frequency f2 to the stylus 2 (2C) detected already. The reason whya forward time slot as near as possible to a time point at which anuplink signal US is transmitted from among the 20 time slots S0 to S19is used is that it is intended to perform such control that, even ifonly one blank period BP can be obtained within an a refresh cycle VT, adownlink signal DS from the stylus 2 is received at a time point thatmay be included in a blank period BP with possibility as high aspossible.

The command CC_UP may include a type of a signal to be transmitted suchthat the data signal OD_DP is included in the time slot S2 and theposition signal D_DP is included in the time slot S4.

Where a plurality of blank periods BP exist in one refresh cycle VT, anuplink signal US may be transmitted within at least one blank period BPto wait for a response of a downlink signal DS, and a command CC_UP maybe transmitted such that a data signal OD_DP is transmitted within adifferent blank period BP.

As described above, according to the position inputting system 1, sensorcontroller 31 and stylus 2 as well as the method performed by themaccording to the present embodiment, since the sensor controller 31acquires a refresh cycle VT at present of the liquid crystal panel 33,it is possible for the sensor controller 31 to transmit an uplink signalUS, which makes a reference for synchronization corresponding to theacquired refresh cycle VT, to the stylus 2. Accordingly, it is possibleto convey a preferable transmission timing of a signal according to astate of the liquid crystal panel 33 to the stylus 2, which sends back adownlink signal DS at a timing designated as the reference time pointfor synchronization given by the uplink signal US. Especially, a signaltransmitted from the stylus 2 that is in a pen down operated state canbe detected at an early stage within a period within which the detectionis not influenced by an action of the liquid crystal panel 33.

Now, a second embodiment of the present disclosure is described. Aprincipal difference between the position inputting system 1 of thepresent embodiment and the position inputting system 1 according to thefirst embodiment is that a row electrode group 45 of a sensor board 34is used commonly as a common electrode of a liquid crystal panel 33,namely, that a sensor board 34 (or liquid crystal panel 33) of the incell type is used. In the following, common constituent elements betweenthe present embodiment and the first embodiment are denoted by likereference symbols and description of them is omitted, and description isgiven principally of the different of the present embodiment from thefirst embodiment.

FIGS. 9A and 9B are a schematic views depicting a structure of theliquid crystal panel 33 serving also as the sensor board 34 according tothe present embodiment. As depicted in FIG. 9A, the liquid crystal panel33 serving also as the sensor board 34 has a row electrode group 45formed on an upper face of a liquid crystal layer 50. As depicted inFIG. 9B, the row electrode group 45 is configured from a plurality ofrow electrodes 45 a to 45 c extending in a Y direction (one direction ina display face of the liquid crystal panel 33). It is to be noted that,although the tree row electrodes 45 a to 45 c are exemplified here, therow electrode group 45 is actually configured from a greater number ofrow electrodes.

The row electrode group 45 serves, when a signal is to be transmittedtoward the stylus 2 and a finger touch is to be detected, astransmission electrodes (Tx), but serves, when a signal from the stylus2 is to be received, as reception electrodes (Rx), as described in thefirst embodiment. Further, the row electrode group 45 serves also ascommon electrodes of the liquid crystal panel 33, and when the liquidcrystal panel 33 is driven, a fixed potential Vcom is supplied to therow electrode group 45. The three roles described above of the rowelectrode group 45, namely, the role as the transmission electrodes(Tx), the role as the reception electrodes (Rx) and the role as commonelectrodes (Vcom) of the liquid crystal panel 33 are implemented by timedivisionally.

As an upper layer on the row electrode group 45, a color filter glassplate 51 is arranged with a transparent insulating layer not depictedinterposed therebetween, and the column electrode group 46 is arrangedon an upper face of the color filter glass plate 51. As depicted in FIG.9B, the column electrode group 46 is configured from a plurality ofcolumn electrodes 46 a to 46 c extending in an X direction (directionorthogonal to the Y direction in the display face of the liquid crystalpanel 33). It is to be noted here that, although the three columnelectrodes 46 a to 46 c are exemplified, the column electrode group 46is actually configured from a greater number of column electrodes. Thecolumn electrode group 46 does not serve as electrodes of the liquidcrystal panel 33, but normally functions as reception electrodes (Rx)similarly to the column electrode group 46 described hereinabove inconnection with the first embodiment. As an upper layer on the columnelectrode group 46, a polarizer 52 is arranged with a transparentinsulating layer not depicted interposed therebetween.

FIG. 10 is a schematic block diagram depicting function blocks of acontrol device 60 provided in the electronic apparatus 3 according tothe present embodiment. As recognized through comparison of FIG. 10 withFIG. 3, in the electronic apparatus 3 according to the presentembodiment, the sensor controller 31, liquid crystal driving circuit 32and electronic apparatus control circuit 30 that are provided separatelyfrom each other in the first embodiment are incorporated as a singlecontrol device 60.

The control device 60 is configured including a control circuit 61 andan indicator detection circuit 62 in addition to the oscillation circuit40, transmission circuit 41 and reception circuit 42 describedhereinabove in connection with the first embodiment. The control circuit61 first has functions of the electronic apparatus control circuit 30and the liquid crystal driving circuit 32 described hereinabove inconnection with the first embodiment. In particular, the control circuit61 has a function for generating a driving signal LD describedhereinabove on the basis of a video signal V obtained by reproducing avideo image signal recorded, for example, on a storage medium notdepicted and supplying the driving signal LD to the liquid crystal panel33.

The control circuit 61 has also a function as a refresh cycleacquisition circuit 44 described hereinabove in connection with thefirst embodiment. In particular, the control circuit 61 has a functionfor extracting a refresh cycle VT indicative of a cycle of control ofthe liquid crystal panel 33 and a blank period BPa that is a periodwithin which the appearance frequency of liquid crystal noise LCDnz islow. However, since, different from the refresh cycle acquisitioncircuit 44, the control circuit 61 itself generates a driving signal LD,the process for extracting a refresh cycle VT and a blank period BPa iscompleted inside the control circuit 61 and it is not necessary tomonitor the liquid crystal noise LCDnz.

Therefore, the blank period BPa according to the present embodiment is aperiod different from the blank period BP in the first embodiment. Inparticular, as described hereinabove with reference to FIG. 5, the blankperiod BP in the first embodiment is a period within which the liquidcrystal driving circuit 32 generates a driving signal LD correspondingto a vertical direction non-displaying area NDA and is a periodcorresponding to the vertical blanking period VB.

In contrast, the blank period BPa in the present embodiment is a periodwithin which a driving process for a pixel is not performed within thelatter half of a horizontal blanking period HB (Horizontal Blanking),namely, within a period within which the pixel of a driving target isreturned from the right end to the left end of the screen. Since theblank period BPa is a very short time period in comparison with theblank period BP, this cannot be utilized effectively in the firstembodiment in which the sensor board 34 of a system of the out cell typeis implemented by an IC in which the sensor controller 31 and the liquidcrystal driving circuit 32 are separate from each other. However, thiscan be utilized effectively in the present embodiment in which thesensor board 34 of a system of the in cell type (or a system of the oncell type) that is configured from an integrated circuit in which thesensor controller 31 and the liquid crystal driving circuit 32 areintegrated with each other and can adjust the refresh timing strictly isimplemented. Although details are hereinafter described, the blankperiod BPa appears many times repetitively within one refresh cycle VTfrom its nature. In the present embodiment, each of the blank periodsBPa appearing many times in this manner is enumerated as a blank periodBP that appears within a cycle of the refresh rate Rr to implementcommunication between the control device 60 as the sensor controller 31and the stylus 2.

FIG. 11A is a view depicting an example of arrangement of a blank periodBPa in the present embodiment. A refresh cycle VT corresponds to a timeperiod (image frame time period) within which displaying of one imageframe is performed as illustrated also in FIG. 7, and as depicted inFIG. 11A, the refresh cycle VT is configured so as to start togetherwith activation of a video image synchronizing signal Vsync that is apulse signal. In the example of FIG. 11A, the refresh cycle VT includesa first number of (525) horizontal blanking periods HB, the latter halfof each of the horizontal blanking periods HB can be utilized as a blankperiod BPa. Accordingly, 525 blank periods BPa are arranged discretelyin an equidistantly spaced relationship from each other in one refreshcycle VT. Since it is necessary to drive a pixel at a timing other thanthe blank period BPa, the potential of the row electrode group 45 isfixed to the fixed potential Vcom described hereinabove. Accordingly,the row electrode group 45 cannot be used for the object of detection ofa finger touch, transmission of a signal toward the stylus 2, receptionof a signal from the stylus 2 and so forth. On the other hand, within ablank period BPa, the potential of the row electrode group 45 is notfixed particularly. Therefore, the control device 60 is configured suchthat it executes actions as the sensor controller 31 describedhereinabove in connection with the first embodiment such as detection ofa finger touch, transmission of a signal toward the stylus 2, receptionof a signal from the stylus 2 and so forth utilizing the blank periodBPa. It is to be noted that, as regards the number or the arrangementmethod of blank periods BPa within one refresh cycle VT, various onesmay available such that they increases as the resolution with which theyare compatible becomes higher like quadruple/quarter full highdefinition (QHD) or full high definition (HD) or conversely the numberof blank periods PBa is intensively reduced to several tens.

Referring back to FIG. 10, the control circuit 61 has stored therein inadvance a plurality of prescribed refresh cycles VT and arrangementmethods of a plurality of prescribed blank periods BPa and selects onerefresh cycle VT and one arrangement method in order to generate adriving signal LD. As a concrete example, the control circuit 61 hasstored therein in advance two refresh cycles VT of 60 Hz and 48 Hz, andwhere the liquid crystal panel 33 is connected to an AC power supply,the control circuit 61 selects 60 Hz, but where the liquid crystal panel33 is driven by a battery, the control circuit 61 selects 48 Hz. Thereason why the refresh cycle VT is lowered where the liquid crystalpanel 33 is driven by a battery in this manner is that it is intended toreduce the power consumption. Further, as an arrangement method of theblank period BPa, the control circuit 61 stores an arrangement method inwhich a first number of (for example, 525) blank periods BPa arearranged in one refresh cycle VT and another arrangement method in whicha second number (number different from the first number) of blankperiods BPa are arranged within one refresh cycle VT, and selects one ofthe arrangement methods in response to a type of the liquid crystalpanel 33 or the like. The control circuit 61 generates a driving signalLD in response to the selected refresh cycle VT and arrangement methodof the blank period BPa and supplies the selected refresh cycle VT andarrangement method of the blank period BPa to the indicator detectioncircuit 62.

The indicator detection circuit 62 performs detection of a finger touch,transmission of a signal toward the stylus 2, reception of a signal fromthe stylus 2 and so forth utilizing a plural number of blank period BPaincluded in a refresh cycle VT. The indicator detection circuit 62 isconfigured such that it repetitively performs the mentioned processes inone set in a circuit of one refresh cycle VT.

FIGS. 11B and 11C are views depicting examples of a manner of use of theblank period BPa by the indicator detection circuit 62 in the case wherea first number L1 (as an example, L1=525) of blank periods BPa arearranged within one refresh cycle VT. In FIGS. 11A and 11C, time periodsT1 to T525 individually corresponding to the first number L1 of blankperiods BPa and communication performed within individual blank periodsBPa are depicted. FIG. 11B depicts an example before a stylus 2 isdetected, and FIG. 11C illustrates allocation of transmission of Nposition signals D_DP and M data signals OD_DP after a stylus 2 isdetected.

First, when a stylus 2 is not detected as yet, the indicator detectioncircuit 62 transmits an uplink signal US in which a search pattern D_UPis included at a plurality of time periods T1, T129, T257, . . . , T513as depicted in FIG. 11B. This search pattern D_UP includes a sequencenumber indicative of what numbered search pattern the search patternD_UP is such that a stylus 2 receiving this can acquire a reference timepoint for a refresh cycle VT.

FIG. 12 is a view depicting an example of a configuration of the uplinksignal US configured in this manner. The uplink signal US according tothe example of FIG. 12 is configured including, in order from the top,two auxiliary uplink signals USsub, three command signals CC0 to CC2 anda cyclic redundancy code CRC generated from the command signals CC0 toCC2.

One auxiliary uplink signal USsub is a signal including a search patternD_UP of one bit known in advance to a stylus 2. The uplink signal USincluding a search pattern D_UP or a command CC_UP of a plurality ofbits is an uplink signal US that is to make a reference forsynchronization corresponding to the refresh cycle VT of the liquidcrystal panel 33 at present similarly as in the first embodiment, andthe auxiliary uplink signal USsub plays a role of notifying a stylus 2of individual time points of a plurality of existing individual blankperiods BPa and transmission timings of the downlink signal DS withinthe individual blank periods BPa. This is because it is intended tonotify a stylus 2 of individual patterns of blank periods BPa, whichbecome different depending upon the situation of liquid crystal driving,without the necessity for sharing the individual patterns with thestylus 2 in advance. One auxiliary uplink signal USsub is a signal for ashort time period in comparison with the uplink signal US, and itbecomes possible to receive a downlink signal DS within one blank periodBPa.

Although the blank period BPa in the second embodiment is a short timeperiod in comparison with the blank period BP in the first embodiment,since the auxiliary uplink signal USsub is a signal of a time lengthcorresponding to one bit, a time period within which the stylus 2transmits a downlink signal DS in response to the auxiliary uplinksignal USsub can be secured within one blank period BPa.

It is to be noted that the auxiliary uplink signal USsub is transmittedin a state in which a frequency of a signal generated by a spread codeof a predetermined chip number is spread. The stylus 2 is configuredsuch that, by executing a correlation process for a known spread codetransmitted in this manner, arrival of the auxiliary uplink signal USsubis detected. The reason why the auxiliary uplink signal USsub istransmitted twice is that it is intended to make it possible for thestylus 2 to distinguish an uplink signal US for identifying a frame ofthe refresh cycle VT and an auxiliary uplink signal USsub for indicatingan individual blank period BPa from each other.

The command signals CC0 to CC2 are signals each indicating a commandCC_UP to be conveyed to the stylus 2. Though not depicted in FIG. 12,also the command signals CC0 to CC2 are transmitted in a state in whichthey are spread by a spread code of a predetermined chip numbersimilarly to the auxiliary uplink signal USsub. It is to be noted thatthe information amount indicated by each of the command signals CC0 toCC2 differs depending upon a manner of use of the spread code. Forexample, where one bit is represented by inversion/non-inversion of thespread code, each of the command signals CC0 to CC2 representsinformation of one bit. On the other hand, where a spread code is usedby cyclically shifting, each of the command signals CC0 to CC2 canrepresent a greater number of bits. In any case, the stylus 2 has storedin advance therein all spread codes that may possibly be received and isconfigured such that, by executing a correlation process between each ofthe spread codes and a reception signal, it receives the command signalsCC0 to CC2. The command CC_UP conveyed through the command signals CC0to CC2 includes information indicative of a refresh cycle VT (forexample 48 Hz or 60 Hz), information indicative of an arrangement methodof the blank period BPa (for example, whether the first number or thesecond number of blank periods BPa are arranged within one refresh cycleVT), information indicative of data to be sent from the stylus 2 to thecontrol device 60 (that one of operation state data OD and configurationdata CD described hereinabove in connection with the first embodiment,which is required by the control device 60), information indicative of ablank period BPa to be used for transmission of data by the stylus 2 andso forth.

The cyclic redundancy code CRC is a code indicative of a remainder whendata indicated by the command signals CC0 to CC2 is regarded as anumerical value and this is divided by a predetermined constant.

Referring back to FIG. 11B, when a stylus 2 is not detected as yet,within the time periods T2 to T128 and so forth other than the timeperiods T1, T129, . . . , T513, the indicator detection circuit 62performs transmission of an auxiliary uplink signal USsub. The substanceof the auxiliary uplink signal USsub transmitted here is same as that ofthe auxiliary uplink signal USsub within the uplink signal US describedhereinabove with reference to FIG. 12. Though not depicted, theindicator detection circuit 62 performs such transmission of a singleauxiliary uplink signal USsub at least once at the top of all of thetime periods including those after detection of a stylus 2. Bytransmitting an uplink signal US and an auxiliary uplink signal USsub incombination in this manner, while a command CC_UP is conveyed to thestylus 2 by the uplink signal US, by receiving a position signal D_DP atan early stage from the stylus 2 that receives the auxiliary uplinksignal USsub, the control device 60 can detect the stylus 2 as early aspossible.

The stylus 2 receiving the auxiliary uplink signal USsub transmits aposition signal D_DP for notifying the control device 60 of presence ofthe stylus 2 itself at an early stage. The indicator detection circuit62 that receives the position signal D_DP from the stylus 2 determinesthat the stylus 2 is detected already and changes the method of use oflater time periods as depicted in FIG. 11C. In particular, only the timeperiod T1 positioned at the top of one frame is used as the “first blankperiod” within which the uplink signal US described hereinabove is to betransmitted, and at least one of the remaining time periods is used asthe “second blank period” within which the downlink signal DS is to betransmitted by the stylus 2. In the example of FIG. 11C, the timeperiods to be used as the “second blank period” within L1 blank periodsare the time periods T2 to T128, T130 to T256 and so forth. Moreparticularly, totaling N time periods including N1 time periods of thetime periods T2 to T5 and N2 time periods T130 to T133 and so forth areutilized by the stylus 2 to transmit a position signal D_DP. Meanwhile,totaling M time periods including M1 time periods T6 to T128, M2 timeperiods T134 to T256 and so forth are utilized by the stylus 2 totransmit a data signal OD_DP including operation state data OD and soforth. In the following description, a data signal OD_DP transmittedwithin an mth (m is an integer from 1 to 492) time period among the Mtime periods is sometimes represented as data signal Dm as depicted inFIG. 11C. The other time periods are used by the indicator detectioncircuit 62 to detect a finger touch.

FIG. 13 illustrates an example of the auxiliary uplink signal USsub andthe downlink signal DS in the case where the stylus 2 performstransmission of the data signal OD_DP within the time period T6 as anexample. Though not depicted, this similarly applies also to the othercase in which the stylus 2 performs transmission of the data signalOD_DP within any other time period.

As depicted in FIG. 13, at the top of the time period T6, an auxiliaryuplink signal USsub including a search pattern D_UP of one bit istransmitted once by the indicator detection circuit 62. In response toreception of the auxiliary uplink signal USsub once, the stylus 2 startstransmission of a data signal OD_DP within the remaining time period ofthe blank period BPa. For example, data data1 to data4 of four bits aretransmitted at once.

Referring back to FIGS. 11A, 11B, and 11C, in the example of FIG. 11C,492 time periods for transmitting a data signal OD_DP are secured. Thestylus 2 is configured such that it transmits data of the first type(for example, the configuration data CD) within the M1 time periods fromamong the 492 time periods and transmits operation state data OD withinthe M2 (M2≥0) time periods. This is described below in connection with aparticular example.

FIG. 14A depicts an example where M1=0 and M2=492. In the presentexample, data S1 and S2 of two bits indicative of on/off states of theoperation inputting circuit 26 depicted in FIG. 2 and data indicative ofa writing pressure F are transmitted using six data signals D1 to D3.

In particular, the data S1 indicative of an on/off state of theoperation inputting circuit 26 is transmitted using the data data3 anddata4 of the data signal D1. Consequently, an on/off state of theoperation inputting circuit 26 is conveyed to the control device 60twice within one refresh cycle VT. However, this is a configuration forproviding redundancy. The writing pressure F is transmitted using thedata data1 to data4 of the data signal D2 and the data data1 to data4 ofthe data signal D3.

Here, as exemplified in FIG. 14A, the data S1 and the writing pressure Fmay be transmitted from the stylus 2 to the control device 60 by thenumber of times equal to or more than twice within one refresh cycle VT.Consequently, since the control device 60 can receive the data S1 andthe writing pressure F with a higher frequency, it is possible toreproduce the width of a handwriting of the stylus 2 with a higherdegree of accuracy. In this case, preferably the transmission timing ofthe data S1 and the writing pressure F is set such that the data S1 andthe writing pressure F are transmitted individually after equal timeintervals.

FIG. 14B depicts an example in which M1=5 and M2=2. In the presentexample, the stylus identifier SID and the writing pressure F aretransmitted using all of the data signals D1 to D7.

More particularly, first the stylus identifier SID is transmitted usingthe data signals D1 to D5. However, since the data amount is excessivelygreat and the data cannot be transmitted only within one refresh cycleVT, it is transmitted over a plurality of successive refresh cycles VT.On the other hand, the writing pressure F is transmitted using the datasignals D6 and D7. Consequently, in the present example, data for eightbits indicative of the writing pressure F is transmitted once withinevery refresh cycle VT.

Here, the stylus identifier SID is information which may be sent onlyonce when the indicator detection circuit 62 detects a stylus 2.Accordingly, initially when a stylus 2 is detected by the indicatordetection circuit 62, after the stylus 2 transmits its stylus identifierSID once using the time periods as depicted in FIG. 14B, the stylus 2preferably uses also the data signals D1 to D5 for transmission of thewriting pressure F. By this, after the stylus identifier SID is conveyedonce to the control device 60, it becomes possible to send the writingpressure F with a high frequency, and also it becomes possible to notifythe control device 60 of an on/off state of the operation inputtingcircuit 26 or a state of the battery.

Now, processes performed by the indicator detection circuit 62 and thestylus 2 according to the present embodiment are described moreparticularly again with reference to respective processing flowdiagrams.

FIG. 15 is a processing flow diagram illustrating processes performed bythe indicator detection circuit 62. Although this processing flowassumes the arrangement method of the blank period BPa depicted FIGS.11B and 11C, also where a different arrangement method is used, theprocessing flow similarly applies although processes performed withinindividual time periods are replaced.

The indicator detection circuit 62 first acquires a refresh cycle VT ofthe liquid crystal panel 33 and an arrangement method of the blankperiod BPa within the refresh cycle VT (S1). Then, the indicatordetection circuit 62 uses the time period T1 to transmit an uplinksignal US including a command CC_UP that indicates the acquired refreshcycle VT and arrangement method of the blank period BPa (S2).Thereafter, within the next time period T2, the indicator detectioncircuit 62 transmits an auxiliary uplink signal USsub and executesdetection of a position signal D_DP transmitted from an unknown stylus 2using all of the electrodes that configure the row electrode group 45and the column electrode group 46 (full scan) (S3).

The indicator detection circuit 62 decides whether or not a positionsignal D_DP is detected (S4), and if it decides that a position signalD_DP is detected, then it sets a pen detection flag (S5) and analyzesthe position of the stylus 2 from the detected signal (S6). On the otherhand, if it is decided at S3 that a position signal D_DP is notdetected, then the indicator detection circuit 62 resets the pendetection flag (S7). It is to be noted that the pen detection flag is aninternal flag of the indicator detection circuit 62, and while a stylus2 remains detected, the pen detection flag indicates the set state, butwhile a stylus 2 is not detected, the pen detection flag indicates thereset state.

The process at S2 from among the described above is performed, when astylus 2 is not detected as yet, similarly as in the time period T1,also within the other time periods T129, T257, T385 and T513 allocatedto transmission of the uplink signal US. On the other hand, if a stylus2 is detected already, then the process at S2 is not performed withinthe other time periods T129, T257, T385 and T513. Further, the processesat S3 to S6 are performed similarly as in the time period T2 also withinthe other time periods T3 to T5, T130 to T133, T258 to T262 and T386 toT389 allocated to reception of the position signal D_DP.

Within the time period T6, the indicator detection circuit 62 firstconfirms the pen detection flag (S8), and if the pen detection flag isin the set state (namely, if a stylus 2 is detected), then the indicatordetection circuit 62 performs a data reception process (S9). On theother hand, if the pen detection flag is in the reset state, then theindicator detection circuit 62 performs only transmission of anauxiliary uplink signal USsub (S10).

FIG. 16 is a processing flow diagram illustrating details of the datareception process performed at S9. As depicted in FIG. 16, the indicatordetection circuit 62 first transmits an auxiliary uplink signal USsuband executes detection of a data signal OD_DP (S20) utilizing onlyelectrodes in the proximity of the position detected at S6 from withinthe row electrode group 45 and the column electrode group 46 (localscan). Then, the indicator detection circuit 62 decides whether or notsome signal is detected as a result of the execution of the detection(S21). Then, if it is decided that some signal is detected, then theindicator detection circuit 62 demodulates the detected signal toacquire the data transmitted from the stylus 2 (S22), whereafter theindicator detection circuit 62 ends the data reception process. On theother hand, if it is decided that no signal is detected, then theindicator detection circuit 62 particularly performs nothing and endsthe data reception process.

Referring back to FIG. 15, the processes at S8 to S10 are performedsimilarly as in the time period T6 also within time periods actuallyused for reception of a data signal OD_DP from among the other timeperiods T6 to T128, T134 to T256, T262 to T384 and T390 to T512allocated to reception of the data signal OD_DP.

Within the time period T514, the indicator detection circuit 62 performsdetection of a finger touch using all of the electrodes configuring therow electrode group 45 and the column electrode group 46 (full scan)(S11).

The indicator detection circuit 62 decides whether or not a signal of afinger touch is detected by the full scan at S11 (S12), and if it isdecided that a signal of a finger touch is detected, then the indicatordetection circuit 62 analyzes the position of the finger from thedetected signal (S13). On the other hand, if it is decided at S12 that asignal of a finger touch is not detected, then the indicator detectioncircuit 62 advances its processing to a next time period withoutperforming any process especially.

The processes at S11 to S13 are performed similarly as in the timeperiod T514 also within the other time periods T513 to T525 allocated todetection of a finger.

In this manner, the indicator detection circuit 62 repetitively performsprocesses allocated to the time periods T1 to T525 depicted in FIGS.11A, 11, and 11C in the order of the time periods T1 to T525. Further,if a new refresh cycle VT is entered, then the processes beginning withthe process at S1 are repeated. Consequently, acquisition of a refreshcycle VT and an arrangement method of the blank period BPa, transmissionof an uplink signal US, detection and position derivation of a stylus 2,reception of a data signal OD_DP transmitted from the stylus 2, anddetection and position derivation of a finger touch are repeatedtime-divisionally.

FIG. 17 is a processing flow diagram illustrating processes performed bya stylus 2. As depicted in FIG. 17, the stylus 2 first performs sensingof an auxiliary uplink signal USsub (S30) and decides whether or not anauxiliary uplink signal USsub is detected by the sensing (S31). Thestylus 2 repetitively executes the processes at S30 and S31 while thepower supply remains on.

If it is decided at S31 that an auxiliary uplink signal USsub isdetected, then the stylus 2 subsequently performs sensing of an uplinksignal US including a search pattern D_UP (S32) and decides whether ornot an uplink signal US is detected by the sensing (S33). This processis in short a process of deciding whether an auxiliary uplink signalUSsub detected at S30 is transmitted alone or is part of an uplinksignal US (refer to FIG. 12). If it is decided at S33 that an uplinksignal US is not detected, then the processing returns to S30, at whichthe stylus 2 performs sensing of a next auxiliary uplink signal USsub.

If it is decided at S33 that an uplink signal US is detected, then thestylus 2 subsequently analyzes a command CC_UP included in the detecteduplink signal US and updates downlink parameters on the basis of aresult of the analysis (S34). The downlink parameters are in shortvarious kinds of information included in the command describedhereinabove, namely, information indicative of a refresh cycle VT (forexample, 48 Hz or 60 Hz), information indicative of an arrangementmethod of the blank period BPa (for example, whether the first number orthe second number of blank periods BPa are to be arranged within onerefresh cycle VT), information indicative of data to be sent from thestylus 2 to the control device 60 (that one of the operation state dataOD and the configuration data CD described hereinabove in connectionwith the first embodiment which is required by the control device 60),information indicative of a blank period BPa to be used for transmissionof data by the stylus 2 and so forth, and the stylus 2 retains thereceived downlink parameters until new downlink parameters are receivedsubsequently.

Then, the stylus 2 executes sensing of an auxiliary uplink signal USsubagain (S35) and decides whether or not an auxiliary uplink signal USsubis detected by the sensing (S36). As a result, if it is decided that anauxiliary uplink signal USsub is detected, then the stylus 2 performstransmission of a downlink signal DS, which is a position signal D_DP ora data signal OD_DP that includes data indicated by the downlinkparameters at a timing according to the auxiliary uplink signal USsub(S37).

If it is decided at S36 that an auxiliary uplink signal USsub is notdetected, then the stylus 2 decides whether or not a transmission timingindicated by the downlink parameters comes (S38), and if it is decidedthat a transmission timing comes, then the stylus 2 performstransmission of a downlink signal DS (S39). This process is a processfor preventing transmission of a downlink signal DS from being skippedby a reception miss of the auxiliary uplink signal USsub. In particular,the stylus 2 can predict a timing at which a downlink signal DS is to betransmitted next on the basis of the refresh cycle VT and thearrangement method of the blank period BPa included in the downlinkparameters. Therefore, even when an auxiliary uplink signal USsub is notreceived, if the predicted timing comes, then the stylus 2 transmits adownlink signal DS.

If it is decided at S38 that the transmission timing indicated by thedownlink parameters does not come as yet, then the stylus 2 returns itsprocessing to S35, at which it performs sensing of an auxiliary uplinksignal USsub again.

After a downlink signal DS is transmitted at S37 or S39, the stylus 2decides on the basis of the downlink parameters retained therein whetheror not a reception timing of an uplink signal US comes (S40). As aresult, if it is decided that a reception timing does not come, then thestylus 2 returns the processing to S35 in order to transmit a nextdownlink signal DS. On the other hand, if it is decided at S40 that areception timing comes, then the stylus 2 returns the processing to S30.Consequently, similar processes are repeated for every refresh cycle VT.

As described above, with the position inputting system 1, sensorcontroller 31, and stylus 2 as well as the method performed by themaccording to the present embodiment, since the control device 60 as asensor controller acquires a refresh cycle VT at present of the liquidcrystal panel 33, it is possible for the control device 60 to transmitan uplink signal US, which makes a reference for synchronizationcorresponding to the acquired refresh cycle VT, to the stylus 2.Accordingly, it is possible to convey a preferable transmission timingof a signal according to a state of the liquid crystal panel 33 to thestylus 2.

Further, since the uplink signal US includes information indicative ofan arrangement method of the blank period BPa, the stylus 2 can transmita downlink signal DS within a blank period BPa in which noise is low.

Although preferred embodiments of the present disclosure are described,the present disclosure is not limited to the embodiments at all, and itis a matter of course that the present disclosure can be carried out invarious modes without departing from the subject matter thereof.

For example, while the second embodiment described above is directed toan example in which the indicator detection circuit 62 transmits anauxiliary uplink signal USsub at the top of each time period, suchtransmission of an auxiliary uplink signal USsub is not alwaysnecessary. In particular, since a refresh cycle and an arrangementmethod of the blank period BPa are conveyed in advance to the stylus 2by an uplink signal US as described hereinabove with reference to FIG.17, the stylus 2 can know a start timing of each time period even if anauxiliary uplink signal USsub is not available. Accordingly, even if thestylus 2 does not receive an auxiliary uplink signal USsub, it canperform transmission of a downlink signal DS at an appropriate timing.Since there is the possibility in the first place also that an auxiliaryuplink signal USsub may fail to be received, preferably it is positionedas an element for auxiliarily conveying a start of a time period.

Since transmission of the auxiliary uplink signal USsub is arbitrary inthis manner, the command CC_UP included in the uplink signal US mayinclude information indicative of whether or not the indicator detectioncircuit 62 is to perform transmission of an auxiliary uplink signalUSsub. By referring to this information, the stylus 2 can determinewhether or not, when a downlink signal DS is to be transmitted, it is towait an auxiliary uplink signal USsub.

It is to be noted that, while the foregoing embodiments are describedtaking the liquid crystal panel 33 as an example, the present disclosurecan be applied also to display panels for which a display panel of adifferent type such as an organic EL panel is applied. Moreparticularly, the present disclosure can be applied to a bidirectionalcommunication system that uses an active stylus utilized together with adisplay panel in which each cycle of a refresh rate includes a displayrefresh period and one or more blank periods.

DESCRIPTION OF REFERENCE SYMBOLS

-   1 Position inputting system-   2 Stylus-   3 Electronic apparatus-   20 Electrode-   21 Transmission/reception switching circuit-   22 Oscillation circuit-   23 Transmission circuit-   24 Reception circuit-   25 Operation information detection circuit-   26 Operation inputting circuit-   27 Configuration information storage circuit-   28 Communication control circuit-   30 Electronic apparatus control circuit-   31 Sensor controller-   32 Liquid crystal driving circuit-   33 Liquid crystal panel-   34 Sensor board-   35 Operation panel-   40 Oscillation circuit-   41 Transmission circuit-   42 Reception circuit-   43 Indicator detection circuit-   44 Refresh cycle acquisition circuit-   45 Row electrode group-   45 a to 45 c Row electrode-   46 Column electrode group-   46 a to 46 c Column electrode-   47 Transmission/reception switching circuit-   50 Liquid crystal layer-   51 Color filter glass plate-   52 Polarizer-   60 Control device-   61 Control circuit-   62 Indicator detection circuit-   700 Transmission timing of uplink signal US-   701, 702 Transmission timing of configuration data CD and operation    state data OD-   719 Response timing to uplink signal US-   BP, BPa Blank period-   CC_UP Command-   CD Configuration data-   CRTbl Communication resource table-   D_DP Position signal (response signal)-   D_UP Search pattern-   DA Display area-   DS Downlink signal-   F_sel Frequency setting signal-   HB Horizontal blanking period-   HI Horizontal synchronization cycle-   HSYNC Horizontal synchronizing signal-   LCDnz Liquid crystal noise-   LD Driving signal-   ND Noise period-   NDA Vertical direction non-displaying area-   NF Noise-free period-   NP Noise period-   OD Operation state data-   OD_DP, D1 to D492 Data signal-   Pos Position information-   Rr Refresh rate-   S_sel Switching signal-   US Uplink signal-   USsub Auxiliary uplink signal-   V Video signal-   VB Vertical blanking period-   Vcom Fixed potential-   Vsync Video image synchronization signal-   VT, VT1, VT2 Operation period

The invention claimed is:
 1. A method implemented by a stylus and asensor controller, comprising: the sensor controller, prior to detectingthe stylus, transmitting an uplink signal (US) a plurality of timeswithin a first frame, the uplink signal (US) including synchronizationreference timing information; the stylus, in response to detecting atleast one of the uplink signals (US) from the sensor controller,transmitting a downlink signal (DS); and the sensor controller, inresponse to detecting the downlink signal (DS) from the stylus and in asecond frame after the first frame, transmitting an uplink signal (US),which includes the synchronization reference timing information, areduced number of times per frame which is less than the plurality oftimes.
 2. The method of claim 1, wherein the uplink signal (US)transmitted the plurality of times includes information indicating howmany times the uplink signal (US) has been transmitted within the firstframe.
 3. The method of claim 1, wherein a frame cycle corresponds to arefresh cycle (VT) of a display coupled to the sensor controller.
 4. Themethod of claim 3, wherein the second frame includes a plurality ofblank periods (BP) and a plurality of display periods (DP) of thedisplay.
 5. The method of claim 4, wherein the uplink signal (US)includes information indicating an arrangement method of the blankperiods (BP) within the second frame.
 6. The method of claim 5, whereinthe arrangement method of the blank periods (BP) within the second framehaving a first frame length is different from the arrangement method ofthe blank periods (BP) within the second frame having a second framelength different from the first frame length.
 7. The method of claim 6,wherein the second frame having the first frame length corresponds tothe display operating at 60 Hz, and the second frame having the secondframe length corresponds to the display operating at a rate other than60 Hz.
 8. The method of claim 5, wherein the blank periods (BP) includestylus detection periods and finger detection periods, and the uplinksignal (US) includes information indicating an arrangement of the stylusdetection periods.
 9. A sensor controller for use with a stylus, thesensor controller comprising: transmission circuitry, which, prior todetecting the stylus, transmits an uplink signal (US) a plurality oftimes within a first frame, the uplink signal (US) includingsynchronization reference timing information; and reception circuitry,which, in operation, receives a downlink signal (DS) from the stylusafter the stylus detects at least one of the uplink signals (US);wherein the transmission circuitry, in response to the receptioncircuitry detecting the downlink signal (DS) from the stylus and in asecond frame after the first frame, transmits an uplink signal (US),which includes the synchronization reference timing information, areduced number of times per frame which is less than the plurality oftimes.
 10. The sensor controller of claim 9, wherein the uplink signal(US) transmitted the plurality of times includes information indicatinghow many times the uplink signal (US) has been transmitted within thefirst frame.
 11. The sensor controller of claim 9, wherein a frame cyclecorresponds to a refresh cycle (VT) of a display coupled to the sensorcontroller.
 12. The sensor controller of claim 11, wherein the secondframe includes a plurality of blank periods (BP) and a plurality ofdisplay periods (DP) of the display.
 13. The sensor controller of claim12, wherein the uplink signal (US) includes information indicating anarrangement method of the blank periods (BP) within the second frame.14. The sensor controller of claim 13, wherein the arrangement method ofthe blank periods (BP) within the second frame having a first framelength is different from the arrangement method of the blank periods(BP) within the second frame having a second frame length different fromthe first frame length.
 15. The sensor controller of claim 14, whereinthe second frame having the first frame length corresponds to thedisplay operating at 60 Hz, and the second frame having the second framelength corresponds to the display operating at a rate other than 60 Hz.16. The sensor controller of claim 13, wherein the blank periods (BP)include stylus detection periods and finger detection periods, and theuplink signal (US) includes information indicating an arrangement of thestylus detection periods.
 17. A system comprising: a stylus; and asensor controller, which, prior to detecting the stylus, transmits anuplink signal (US) a plurality of times within a first frame, the uplinksignal (US) including synchronization reference timing information;wherein the stylus, in response to detecting at least one of the uplinksignals (US) from the sensor controller, transmits a downlink signal(DS); and the sensor controller, in response to detecting the downlinksignal (DS) from the stylus and in a second frame after the first frame,transmits an uplink signal (US), which includes the synchronizationreference timing information, a reduced number of times per frame whichis less than the plurality of times.
 18. The system of claim 17, whereina frame cycle corresponds to a refresh cycle (VT) of a display coupledto the sensor controller.
 19. The system of claim 18, wherein the secondframe includes a plurality of blank periods (BP) and a plurality ofdisplay periods (DP) of the display, and the uplink signal (US) includesinformation indicating an arrangement method of the blank periods (BP)within the second frame.
 20. The system of claim 19, wherein the blankperiods (BP) include stylus detection periods and finger detectionperiods, and the uplink signal (US) includes information indicating anarrangement of the stylus detection periods.